Field of the Invention
The present invention relates to film deposition apparatus and method which perform reactive sputtering.
Description of the Related Art
Conventionally, in the field of film deposition (or film preparation) for wide-area substrates such as flat display panel, a solar battery panel, glass for architectural materials, automotive glass and the like, magnetron sputtering using a flat-plate rectangular target has been performed.
In the magnetron sputtering, a magnetic field creator is disposed (or located) on the periphery of the target (mainly at the back side) to cause electrons to perform motion called E×B drift by a magnetic field (B) created by the magnetic field creator and an electric field (E) applied to the target. Thus, the sputtering is performed with high efficiency by increasing the electron density with use of the E×B drift of the electrons.
On the other hand, owing to requests of lowering costs and increasing productivity, reactive sputtering of depositing a compound thin film to a substrate by sputtering a metal target or the like with DC discharge under introduction of a reactive gas (e.g., O2) has been widely used. Here, the compound thin film is used to add an insulating function and an antireflection function to, for example, a glass substrate or a different-use film deposited on the glass substrate.
In the reactive sputtering, it has been known that three states respectively having different film deposition speeds and different film qualities exist as the surface states of a target. The three states include a metal state, a reactive state (compound state) and a transition state between the metal state and the reactive state. In the reactive sputtering, a hysteresis exists in a change of the state at the time when a reactive gas flow rate is changed. As for such a hysteresis phenomenon, the theory of S. Berg and the like of modeling reactive gas balance has been known (see S. Berg, H. O. Blom, T. Larsson, and C. Nender: J. Vac. Sci. Technol. A, 5 (1987), 202).
Incidentally, in the magnetron sputtering using the flat-plate rectangular target, it has been known that the plasma density increases in the vicinity position of the E×B drift of the electrons, the film deposition speed increases at the point where the plasma density increases, and thus the film thickness distribution on the substrate become nonuniform (or uneven). To solve such inconvenience, Japanese Patent Application Laid-Open No. S61-037964 (hereinafter called Patent Literature 1) proposes the method of performing feedback control of a reactive gas flow rate by monitoring plasma emission. This method has been called Plasma Emission Monitoring, Optical Emission Monitoring, or the like (hereinafter, the relevant method is called PEM). To control the film thickness distribution on the substrate, it is important to control the degree of a compound in the target surface by controlling the flow rate of reactive gas. Namely, it is important to control balance between metallization by the sputtering on the target surface and compoundization by the reactive gas.
Japanese Patent Application Laid-Open No. H05-504373 (hereinafter called Patent Literature 2) proposes the film deposition apparatus in which a cylindrical target called a rotary cathode is used instead of a flat-plate rectangular target in order to improve process stability and a use efficiency of materials. In the Patent Literature 2, the conveyance direction of the substrate and the rotation axis of the target are orthogonalized, and the thin film is deposited on the substrate by rotating the target while conveying the substrate. Incidentally, in addition to the rotary cathode, the above cylindrical target is variously called a cylindrical rotary magnetron cathode, a cylindrical cathode, or the like. Also, in case of depositing the thin film on the substrate by the reactive sputtering using the cylindrical target, the film thickness distribution depends on the coating ratio of the compound (e.g., metal oxide) in the target surface.
Japanese Patent Application Laid-Open No. 2012-530851 (hereinafter called Patent Literature 3) proposes the method of controlling the coating ratio of a compound on the surface of a cylindrical target by using the PEM up to now in case of performing the reactive sputtering in the target.
In the Patent Literature 1, although the flat-plate rectangular target is used, the method of adjusting the reactive gas amount supplied from each gas introduction port while measuring plasma emission to uniformize the film thickness distribution on the substrate has been proposed. It is conceivable to control the reactive gas flow rate by the PEM in the cylindrical target, by applying the method of the Patent Literature 1 to the Patent Literature 2.
However, when the reactive gases are supplied to the target from the plurality of the gas introduction ports respectively, these gases supplied from the different gas introduction ports intermix and thus interfere with others. Due to such complicated mutual interference, it was difficult only by control of the reactive gas flow rate to uniformize the degree of the compound on the target surface in the rotation axis direction. Moreover, since the cylindrical target rotates, there was a problem that the degree of the compound on the target surface becomes nonuniform also in the rotation direction and thus the film deposition speed becomes nonuniform. As a result, in the conveyance direction of the substrate and the width direction intersecting the conveyance direction of the substrate, the film thickness distribution of the thin film on the substrate was nonuniform. That is, in order to achieve uniformization of the film thickness distribution on the substrate, it was necessary to uniformize the degree of the compound in the rotation direction (circumferential direction) and the direction of the rotation axis on the target surface.
On the other hand, in the Patent Literature 3, to prevent generation of a striped film, the method of matching the period by which the target voltage is changed with the rotation of the target has been proposed in addition to the flow rate control of the reactive gas. However, although it was possible to prevent that the striped film is generated in the conveyance direction of the substrate, it was necessary to provide another improving method for uniformizing the film thickness distribution in the width direction on the substrate.